SAN FRANCISCO — Expanding further beyond its origins as an app for sharing pretty photos, Instagram said on Wednesday that it will now allow users to post videos up to an hour long, a feature that will thrust it into direct competition with YouTube and its own parent company, Facebook.

At an event in San Francisco that was delayed about 45 minutes because of technical issues, Instagram said it was debuting IGTV, a new video section for videos that are shot vertically — which is how people typically record things on smartphones. The company said it would also begin offering IGTV as its own stand-alone app in the next few weeks.

Facebook acquired Instagram in 2012 for $1 billion when the nascent photo-sharing service had only 30 million users. Since then, Instagram has opened the platform to videos of up to one minute and copied a popular feature of its rival Snapchat by allowing ephemeral posts known as stories.

Instagram said it has a billion monthly users. By comparison, Google’s YouTube platform has said it has 1.9 billion users logging into the service every month, and Facebook — which has itself been pushing consumers to spend more time watching videos — has 2.2 billion monthly users.